Events leading to the onset of various ocular complications are being investigated. Specifically, the studies focus on the role of the enzymes aldose reductase and aldehyde reductase in the onset and progression of retinopathy, cataract, keratopathy, pupil function changes, and iris and ciliary process structural changes associated with diabetes and galactosemia. In addition, methods for either delaying or preventing the onset and progression of these complications through the pharmacological control of these enzymes are being developed. Also being studied are events leading to the formation of several types of cataracts as well as methods for controlling the onset of these cataracts through pharmacological intervention.